Viral infections such as hepatitis C virus (HCV) and Flavivirus are major causes of morbidity and mortality around the world. Chronic infection with HCV, for example, is a major health problem that affects more than 170 million people worldwide and is a causative agent of liver cirrhosis, hepatocellular carcinoma, and liver failure. While treatments exist for HCV, these treatments often have limited efficacy, serious side effects, high expense, and can result in drug resistance. Further, Flaviviruses such as West Nile virus (WNV), Japanese Encephalitis virus, and Dengue virus (e.g., the four known serotypes of Dengue virus (DEN-1-4)) are significant human pathogens that cause millions of infections each year and result in considerable morbidity and mortality. DEN viruses cause a simple and self-limiting disease in humans called dengue fever (DF), which often resolves in a week to 10 days. However, more severe forms of the disease, known as Dengue hemorrhagic fever (DHF) and Dengue shock syndrome (DSS) common in areas endemic to DEN 1-4 lead to considerable morbidity and mortality. According to World Health Organization estimates, 50-100 million cases of DEN infections in tropical and subtropical countries occur each year. WNV was introduced into the western hemisphere during an outbreak in the United States in 1999. In the following years, WNV has spread throughout much of North America and has become a public health concern. Most WNV infections are asymptomatic; however, about 20% of cases are associated with mild flu-like symptoms. A small fraction of these cases progress to more severe clinical manifestations including encephalitis and/or flaccid paralysis. There are no approved vaccines or antiviral therapeutics available for either DEN- or WNV-infected human.
Additionally, fungal infections are also significant causes of death in human and animal populations. Candidiasis is an infection that is caused by fungi and yeasts, and can be life threatening for those with weakened immune systems. While there are treatments for candidiasis, these treatments often result in drug resistance.